Circuit arrangement for amplifying or generating ultra high frequency oscillations



APrll 13, 1948. M. J. o. STRUTT ETAL 2,439,638

CIRCUIT ARRANGEMENT FOR AMPLIFYING OR GENERATING ULTRA HIGH FREQUENCY OSCILLATIONS Filed May 21, 1943 i116. 1. jig. Z.

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Patented pr. 13, 1948 andere CIRCUIT ARRANGEMENT ron AM1 L11FY1`NG on GuNERA'rING ULTRA l HIGH FRE- QUENCY osciLLA'rroNs Maxirniliaan llulius Otto Strutt, Aldert van der Ziel, and Adrianus Johannes Wilhelmus Marie. van Overbeek, Eindhoven, Netherlands, assigniors to Hartford National Bank and Trust Company, Hartford, Conn., as trustee Application May 21, 1943, Serial No. 487,979 In the Netherlands August 20, 1941 Section 1, Public Law 690, August 8, 1946 Patent expires August 20, 19,61

This invention relates to a circuit arrangement for amplifying or generating ultra high-frequency oscillations which comprises a discharge tube having at least a cathode, a signal control electrode, a perforated positive electrodek and two further electrodes.

With ultra-high-frequencies the properties of discharge tubes for amplifying and generating oscillations are greatly diiierent from those with lower frequencies. More particularly in amplifying ultra high-frequencies the fact has to be taken into account that a virtual ohmic resistance having .a comparatively small value occurs between the control grid and the cathode which resistance exerts a strong damping on the input circuit. The presence of this virtual ohmic resistance is mainly due-to'two causes.

'Primarily the comparatively great transit time of the electrons will involve a phase displacement between the alternating control-grid voltage and the electronic stream passing through the apertures of the control grid, which phase displacement involves an influence current to the control grid. This influence current has a component which is in phase with the alternating controlgrid voltage and may be construed as resulting from a virtual ohmic resistance available between the control grid and the cathode. The reciprocal value of this resistance is called transit-time damping or electron damping.

Secondly the natural inductances of the supply conductors to the various electrodes will exhibit a considerable impedance in regard to the oscillations `to be ampliiied, so that high-frequency voltages are set up across these supply conductors, which voltages give rise to currents passing through the natura1 tube capacities and being in phase with the alternating control-grid voltage. The damping of the input circuit thus caused may be'called lead damping.

Theelectron damping and the lead damping are both about proportional to the square of the frequency of the oscillations to be transmitted. At ultra-high frequencies the input damping resulting from both of these components is usually so strong that the impedance of the resonant circuit inserted in the signal control grid circuit is high relatively to the input resistance of the tube. Therefore, the output impedance ofr a stage in cascade circuits is practically solely determined 5 claims. (c1. 1719-171) by the input resistance of the next stage, so'that the attainable amplications per stage substantially corresponds tothe product of mutual conductance and input resistance. In order to obtain suiiicient amplification at ultra-high frequencies the attempts have consequently to be directed to as high an input resistance and mutual conductance as possible.

Recently various proposals have been made to reduce the input damping of amplifying tubes. Thus'for instance, the lead damping can be reduced by making use of a tube having two cathode-supply conductors, one of which is inserted in the input circuit, whereas the other is interposed inthe output circuit. Another expedient to reduce the lead damping consists in the use oi" amplifying tubes comprising two push-pull connected amplifying-systems whose cathodes are connected by as short a lead as possible.

A further improvement of the input damping is possible by taking various measures essentially amounting to back-coupling, for instance by inserting an additional inductance in the screengrid lead. A very suitablemethod of decreasing the input Ydamping consists in that in a tube having two cathode supply leads the inductance of the cathode supply lead interposed in the output circuit and/or the screen-grid/control-grid capacity isincreased artificially.

For a good effect of the steps referred to above for decreasing the input damping it is always necessary, however, that the tube should have a fairly high mutual conductance. A high mutualconductance is necessary also for generating ultra high-frequency oscillations.

However, in amplifying or generating oscillations 'having ultra high-frequencies the effective or dynamic mutual conductance occurring is much lower than the static mutual conductance which is more particularly due to the fact thatl the transit time of the electrons is of the same order of magnitude as the period of the oscillations to be amplied or to be generated.

It has already been proposed to increase the dynamic mutual conductance by connecting the ends of the output impedance respectively to two electrodes which are located in the path of the .bythe electrons'iny less than half a period of the 'oscillations to be amplified or to be generated.

n nin However, since it is not possible to give the dis-- tance between the said electrodes an arbitrarily small value an improvement can thus be obtained, only in a limited range of frequencies.

The present invention has for its purpose to provide a circuit by means of which a high dynamic mutual conductance can be obtained even with still shorter waves.

According to the invention this is achieved in the circuit of the kind referred to above by choosing the biases, the construction and the mutual distance -of the electrodes in such manner that at least substantially all electrons pass through the perforated positive electrode, are reflected by an electrode more remote from the cathode and ance more traverse the positive electrode, whereupon they are either collected or reected again by an electrode located at the cathode side of the positive electrode.

If the reflected electrons are able to approach the signal control-electrode they may sometimes cause an increased input damping or'a decrease in dynamic mutual conductance. Hence, the electrode located at the cathode side of the perforated positive electrode is so positioned and has such a potential that the reflected electrons cannot affect the signal control electrodes. A maximum dynamic mutual conductance is obtained if the biases of the electrodes are so chosen that the time T, which elapses between the moment at which an electron traverses the perforated electrode for the rst time and the moment at which the same electron, after reilection, traverses the perforated electrode again amounts to about a whole number of periods of the oscillations to be taken from the circuit. In this case a less positive auxiliary electrode may still be provided before the perforated positive electrode, and the output energy may be taken from the perforated positive electrode and/or from the reecting electrode and/or from the said auxiliary electrode.

The invention will be more clearly explained by Yreference to the accompanying drawing wherein Fig. 1 discloses certain tube electrodes and circuit connections which will serve to explain the principle underlying the invention; Fig. 2 shows comparative mutual conductance curves of a pentode used in a conventional circuit and of a tube used in a circuit according to the present invention; Fig. 3 will serve to explain the conditions under which a maximum dynamic mutual conductance occurs; and Figs. 4, 5 vand 6 disclose circuit arrangements of various embodiments of the present invention.

Referring first to Fig. 1 there is schematically represented at I0 an electron stream which, being under the control of a signal control electr-ode Il, passes through the apertures of a perforated positive electrode II, is subsequently reiiected by the electrode I2, which is at cathode potential, and traverses the electrode II for the second time. At the cathode side of the electrode II is located a screen-grid I3 which is at cathode potential and reflects the returning electrons for the second time. However, the screen grid I 3 may also have such a potential that the returning electrons are collected by this grid. The electrode II is located about midway between the electrodes I2 and I3.

Fig. 2 shows two graphs illustrating the effectof the invention, The curve I represents the ratio between the dynamic mutual conductance S and the static mutual conductance So as a function of the product fT and holds for a pentode in which the anode has a positive bias and substanencaisse 4 tially all electrons reach the anode, f representing the frequency of the oscillations to be transmitted and T corresponding to twice the time required by the electrons for wandering from the screen-grid to the anode.

The curve II represents the ratio S/So as a function of the product JT when making use of the invention, T representing the time elapsing between the moments at which an electron passes for the first time and for the second time through the electrode II. From the curve II it appears that the dynamic mutual conductance is in each instance a maximum when fT -corresponds to a Whole number. The maximum values of the dynamic mutual conductance far exceed the values that can be obtained by means of a pentode in a normal circuit Varrangement and with the rst two maxima it also exceeds the static mutual conductance; with the first maxima (T=1) it may, for instance, be about 2.5 times as high. If ;fT=l, the time elapsing between the rst and second time the perforated positive electrode is passed by an electron exactly corresponds to one period of the oscillations to be taken from the circuit. Considering that the influence voltage induced in the electrode II by the returning electrons is then completely supported by the influence volt-age induced in the electrode II by the going electrons it will be appreciated that, in effect, a maximum dynamic mutual conductance must occur under these conditions. This Will be more fully explained by reference to Fig. 3.

In Fig. 3 the electrodes II, I2 and I3 are schematically represented. Let it be assumed that an electronic stream controlled by a signal control electrode (not represented) reaches the electrode I3. If the lcontrol voltage is a periodic oscillation the electronic stream consists of a series of succeeding concentrations and deconcentrations of electrons whose alternating current component consists of a series of succeeding positive or negative charges. These charges are represented by small circles in the drawing, in which the minus sign denotes a negative and the plus sign denotes a positive charge. It is now to be taken that the charges consecutively pass from the left to the right one behind the other through the electrode I3 so that the time elapsing between the passage of the charges 2l and 22 amounts to half a period and the time elapsing between the passage of the charges 2| and 23 amounts to a whole period of the oscillations to be amplied.

When the charge 2l travels from the electrode I3 to the electrode I2 a positive image charge is induced in the electrode II upon traversing the latter which charge at rst increases and subsequently decreases again and has a maximum value at the moment at which the charge is at the point denoted by 2|. 'In the position 2| the image charge substantially corresponds again to zero and in the position 2I"' it assumes again a maximum value. If the time elapsing between the positions 2 I and 2 I exactly amounts to one period of the oscillations to be amplified, Which is supposed in the drawing, then, at the same moment at which the charge 2l traverses the electrode I I in a downward direction, the charge 23 will traverse the electrode II in an upward direction, will also induce a positive image charge in this electrode and consequently double the charge already available. As a result of the succeeding negative charges 2|, 23, 25 and so 0n, a voltage represented by the curve III in Fig. 3 will appear in the electrode II.

In the same .Way it .can beexplained that the positive charges 2 2, 2,4 andso :on induce a voltage in the electrode II, which voltage is represented by the curve IV. The resulting voltage variations, for which are ,responsible the influence charges at the electrode II,A are represented by the .curve V which is the resultant of the vcurves Ill and Therefrom it appears that under thesupposed conditions the Various charges per.- fectly Cooperate s o that at rst view a four-fold increase in mutual conductance might4 be expected. Since, however, the dynamic mutual conductance occurring at any moment, such as is indicated by the curve I., is smaller than the Static `mutual conductance, the .dynamic mutual conductance actually occurring under the supposed Conditions is also lower, viz., about 2.5 times as high as the static mutual conductance.

compared with known circuits, in which the obtainable maximum value of the V'dynamic mutual conductance corresponds at the most to the Value i the static mutual conductance, the circuit according to the invention constitutes a great improvement. If, in eiect, a definite minimummutual conductance is required for amplifying ultra high-frequency oscillations a circuit according to the invention permits this minimum mutual conductance still to be attained at a much higher frequency.

Moreover, it appears from the curve II sh'own in Eig. 1 that even if the period of the oscillations toY be amplied is a multiple of the time interval T Considerable maxima occur in the mutual conductance.

sponds to the static mutual conductance. Owing to this the minimum Wavelength, at which' a sui'- ncient mutual conductance is available as yet, is muchl smaller than with the circuitsV hitherto known.

Hereinbefore it has been set out how an amplied voltage is set up at the electrode I'I,"but it will be appreciated th'at, as an alternative, the amplified oscillations may be .taken from any of theelectrodes I2 and I3 andthat a suitable choice of the transit times permits the amplified oscillations to be taken in push-pull from the electrodes I2 and I3.

Fig. l represents an embodiment of the invention which comprises an amplifying tube I5 having a cathode I6, a signal control grid Il, a grid I3, a perforated positive electrode II and a re.- flection electrode I 2. The electrodes l2 and I3 are interconnected and connected throughaconductor 2I to the cathode. Between the signal control grid Il and the cathode I6 is supplied a voltage eg to be amplified having a frequency f. The perforated electrode II is connected to the cathode through the intermediary of a resonant circuit I8 tuned to the frequency f and av source of potential I9 by which the electrode II is given a positive potential. The electronic stream emitted by the cathode I6 is controlled in intensity in the usual way by the signal control electrode I1, as a result of which there occur concentrations and deconcentrations in the electronic stream which, due to the positive potential of the electrodes II, travel in th'e direction thereof. The concentrations and deconcentrations pass through the apertures of the electrode II and are reflected owing to the presence of the electrode I2 having cathode potential so that they pass again through' the apertures of the electrode II. When traversing the electrode II forth and back the concentrations and decon- Thus, for instance, if fT=3 the dy-vl nami mutual conductance substantially correcentrations induce influence charges in the elec trode II, the induced charges amplifying each other, owing to the concentrations and deconcentrations passing forth and back, if the time 5 elapsing between the passage in one and inthe other direction substantially amounts to a whole number of periods Vof the oscillations to be amplied. In this .case a voltage having the frequency of the voltage supplied to the .electrode ITI can be taken from the circuit VI 8, the mutual conductance then being much higher than in the absence of the electrode I2.

Fig. 5 represents another embodiment of the invention in which the ampliiied oscillations are not taken from the perforated electrode but are derived in push-pull from the reilecting electrode and the grid I3 located in front of the electrode II. Furthermore the tube comprisesan electrode which is at a .positivepotential and has 20 ior its purpose to collect the electrons after they have passed for the second time through the grid i3, so that they can no longer affect the control grid I1, i

A still greater increase in dynamic mutual conductance can be obtained by taking care that the concentrations and deconcentrations of electrons do not traverse once but several times the space between the reflecting electrode and the electrode located in front of the perforated positive electrode.

An embodiment making use of this principle is represented in Fig. 6. In this case a discharge tube is used comprising a cathode 20, an electronoptical focussing device 2I, by means of which the beam can be controlled in intensity at the same time, an electron-optical device 23 by which the electron rays lare formed into a beam and accelerated, a grid-shaped electrode I I, a reflecting electrode I2 and a second reecting electrode 40 I2', th'e electrode system II, I2, I2' being solocated relatively to the electronbeam that its axis 22 forms an oblique angle with the direction of the electrodes II, I2, I2. Between the electrode 2| and the cathode 2t is, supplied a voltage to be amplified eg having a frequency f so that concentrations and deconcentrations occur in the electronic stream passing through the electrode II. This electrodeV is .given a positive potential by the battery B. The concentrations and deconcentrations are reflectedr by'the electrode I2 having cathode potential,. pass again through the electrode Il, after. which' they are reflected by the electrode I2' also havingcathode potential, pass again through the electrode II andA so on as indicated by the dash line 24. Finally all electrons reach the positive electrode II. Owing to the concentrations and deconcentrations passing th'rough the electrode Il charges will be induced therein :all of which support each otherl if the timeY elapsing between two moments at which the electrode II is passed by an electron is equal to the period of the oscillations to be amplified. The circuit of the electrode II comprises a circuit I8 which is tuned to the frequency of the oscillations to be amplified and from which are taken the amplified oscillations. As an alternative, however, the output circuit I8 may be connected between the electrodes I2 and I2 and earth, as shown in Fig. 5, or between one of the electrodes I2 or I2 and earth, in which case the electrode II is at cath'ode potential for high frequency.

What we claim is:

1. A circuit arrangement for amplifying or genr erating high frequency oscillations comprising an electron discharge tube having arranged in the order named a cathode, a signal control electrode,

a first reflecting electrode, a perforated electrode and a second reflecting electrode,` means to couple said rst reflecting electrode to said second refleeting electrode, means to maintain said reflecting electrode at cathode potential, and means to apply a positive potential to said perforated electrode, said electrodes being .so constructed, arranged and spaced and saidpositive potential having such value with respect to the cathode that the electrons, at least for the greater part, perform an oscillatory movement through said perforated electrode and within a region defined by said reflecting electrodes to thereby increase the mutual conductance of said tube.

2. A circuit arrangement for amplifying or generating high frequency oscillations, comprising an electron discharge tube having arranged in the order named a cathode, a signal control grid, a reflecting grid, a perforated electrode and a refleeting electrode, means to couple said reflecting grid to said reflecting electrode, means to maintain said reflecting grid and electrode at cathode potential, means to apply a source of positive potential to said perforated. electrode and an output circuit interposed between said perforated electrode and the source of said positive potential, said electrodes being so constructed, arranged and spaced and said positive potential having such value with respect to the cathode that the electrons, at least for the Ygreater part, perform an oscillatory movement through said perforated electrode and within a region defined by said refleeting electrodes to thereby increase the mutual conductance of said tube. Y

3. A circuit arrangement for amplifying or generating high frequency oscillations, comprising an electron discharge tube having arranged in the order named a cathode, a signal control grid, a reflecting grid, a perforated electrode .and a reflecting electrode, means to couple said reflecting grid to said reflecting electrode comprising an output circuit coupled between the reflecting grid and the reflecting electrode, means to maintain said reflecting grid and reflecting electrode at cathode potential and means to apply a positive potential to said perforated electrode, said electrodes being so constructed, arranged and spaced and said positive potential having such value with respect to the cathode that the electrons, at least for the greater part, perform an oscillatory movement through said perforated electrode and within a region defined by said reflecting electrodes to thereby increase the mutual conductance of said tube. r

4. A circuit arrangement for amplifying or generating high frequency oscillations, comprising an electron discharge tube having arranged in the order named a cathode, a signal control grid, a

' Vreflecting grid, a perforated electrode and a refleeting electrode, means to couple said reflecting grid to said reflecting electrodecomprising an output circuit interposed between said reflectinggrid and said ree'cting electrode, means to maintain said reilectinggrid and said reflecting electrode at cathode potential, an electron collecting electrode positioned on the cathode side of vand adjacent said reflecting grid, and means to apply a positive potential to said perforated electrode, said electrodes being so constructed, arranged and spaced and said positive potential havingsuch value with respect to the cathode that the electrons, at least for the greater part, perform an oscillatory movement through said perforated electrode and within a region defined by said reflecting electrodes to thereby increase the mutual conductance of said tube.

5. A circuit arrangement for amplifying or generating high frequency oscillations, comprising an electron discharge tube having arranged in the order named a cathode, a signal control electrode, a beam forming and accelerating electrode, a first reflecting electrode, a perforated electrode and a second reecting electrode, means to couple said first reflecting electrode to said second reflecting electrode, means to maintain said reflecting elec trodes at cathode potential, means to apply'a source of positive potential to. said perforated electrode and an output circuit; `interposed between said perforated electrode and the source of said positive potential, said electrodes being so constructed, arranged and spaced and said positive potential having such value with respect to the cathode that the electrons, atleast for the greater part, perform an oscillatory movement through said perforated electrode and within a region dened by said reflecting electrodes to thereby increase the mutual conductance of said tube.

MAXIMILIAAN JULIUS OTTO STRUTT. ALDERT VAN DER ZIEL. ADRIANUS JOHANNES WILHELMUS MARIE VAN OVERBEEK.

REFERENCES CITED The following references are of record in the file of this patentzrl f UNITED STATES PATENTS 

